Fatigue Assessment for Failed Bridge Deck Closure Pour
After 17 years in service, a 3 ft by 3 ft closure pour section of an Interstate 81 (I-81) bridge deck failed by punching through near Marion, Virginia. Visual inspection noted that there was considerable corrosion on some of the reinforcing bars in the vicinity of the construction joint, while other failure bars had little or no corrosion. Sections of the bridge deck were cut and delivered to Virginia Tech for further investigation.
It was clear from an initial investigation that shrinkage of the deck concrete had caused the construction joints to open and thereby allow water and chlorides to enter the joint. In addition, it was observed that several bars across the closure pour construction joints had suffered significant section loss due to corrosion, but it was not clear if fatigue and strength failure of the reinforcing bars were also contributing factor in the closure pour failure.
To study the problem four fatigue tests and five strength tests performed. The specimens included six slab strips cut from the I-81 bridge deck, with the 3-ft closure pour included, and three additional specimens that were cast in the laboratory to represent a base line for performance. A three-point loading setup was used for both fatigue and strength tests. However, for the final strength and fatigue tests, a jacking system was designed and implemented in an effort to open the closure pour construction joints to simulate the open joints of the I-81 bridge.
The objectives of this research program are to provide a better understanding of the closure pour failure mechanism, develop inspection procedures for Virginia Department of Transportation (VDOT) to assess its bridge inventory containing similar construction joints, and to develop recommendations for future construction of similar construction joints.